Thursday, 25 September 2008

New bits

Over the last few months I have been hunting for parts for K-9 and here is what I have found…

A few posts ago I mentioned that I had bought some windscreen wiper motors. Here they are cleaned and stripped next to a 12V sealed motor cycle battery.The steel turn arm was removed by clamping tightly the turn arm in a vice, getting a friend to help hold onto the motor to prevent it turning as I undid the nut. They are well fixed on!! The brass mounting was removed by removing the small nuts using socket spanner.A bit of CRC was used to ease the nuts off as they had welded on over time. All nuts and bots were retained for future mounting. Then with some more CRC the motor was thoroughly cleaned up.Just for all you car boffins out there... Here is a photo of what they would have looked like in the original car...And this is what I sort of hope to achieve with them, like Robert's K-9.

6 comments:

Hi Issy, You may find that your base gets stcuk easly because of the weight on the free wheel. If you have the space try mounting the Battery on top of the motors, this will improve their grip and should make it easier to drive. I noticed you have a comment on the base board about not reversing one of the motors. What is the problem here?Regards Peter

Sorry I hadn't seen your comment for such a long time! I have been rather slack with my blog, I must admit, being distracted by another new hobby of mine, my motorcycle. :-D

I was planning rather than Robert's one free-wheel mode, to have the two free-wheeled mode at the back like was on the Hero prop, and also on some of the builds on MSN board. I just liked the setup of the motors and battery. However, I will keep in mind the suggestion of the battery over the motors... Although there isn't usually much room because the mechanism for K-9 head mechanism goes in front. Perhaps if he is re-wheel drive... But I have heard then he doesn't have as much turn action then... Decisions, decisions...

The worry about the motor reversal is that, when you flip a windscreen wiper motor, they seem to travel at a different speed then traveling forward. I was worried it would put a strain on the motor. Also I had to work out a way to compensate for the speed difference between the two motors, even though they are exactly the same, but because one if flipped, the speed reduction inside must be different.

I put this question to the boys at the Australian R2D2 forum last year and they said that putting in a speed controller, notably the Sabertooth would eliminate the issue. Also the Sabertooth's are capable of withstanding the brushed motors, unlike many of the hobby style speed controllers.

Putting the drive wheels in the middle would provide more even traction, that is correct. There is however a balance issue. The head is big and contains a lot of extra bits. There is also a motor on the head panel for the up/down motion that needs balancing. The two wheels in the front provide that balance.

You could have a free wheel at the front and at the back with the drive wheels in the middle, but that front wheel will have to take quite a bit of balancing load. If the wheel is small, like most free wheels are, then it may tip if on an angle.

As it is so crammed inside the metal mutt, the battery will have to go where it fits. At the moment it looks like I may be able to get it near the middle, but once again it will have to balance the head. So the weight is looking it might be near the bum of the dog, but not quite to the back because of the free wheel and the camber inside. I also have to leave a bit of room for the tail mechanism. Actually the best way to do it would probably have the wheels in the back with the battery over the top of it, but I don't think that will happen. Also I have heard from other builders that the tuning capacity becomes more limited with that set-up.

On the note of the battery, I think I may go the way of battle droid logic. Have two batteries. One controlling the drive unit, the other the electronics. That way if the drive unit runs down or fails, I can still have it functioning partially, especially if on display or something. Also if the electronics fail, it can still be driven around. It is a heavier/more expensive option, but I would go for two lighter motorcycle batteries then a large motorcycle or car battery.